Conducting police and fire investigations involves recording locations and taking images of objects of interest or detector measurements in crime or fire scenes. It is important to maintain sufficient stand-off distances from such objects so as not to disturb or contaminate the scene, or to expose investigators to hazards. All collected data must be properly recorded including acquisition time, exact locations of the objects and the recording devices to enable reconstruction of the scene, show investigation process, and re-create the most likely scenario that led to the event.
Currently, locations of objects of interest are measured using tape measures, hand held rangefinders, total stations, Global Navigation Satellite System (GNSS) receivers or indoor positioning systems. Images and videos are acquired using hand-held or tripod mounted cameras. Tripod mounted or hand held 3D cameras and 3D scanners are used to capture 3D representations of complete scenes including objects of interest. Location of these objects can be obtained by selecting them in the 3D scans. For conducting police and fire investigations it is preferable to use hand-held or wearable devices that are easy to deliver and operate in the scene, and that do not require complex deployment on a tripod or to be delivered on a mobile platform.
Locations of objects of interest in investigated scenes can be measured from stand-off distances using hand-held ranging devices such as laser rangefinders, if position and orientation of these devices can be determined in a coordinate system associated with the scene. Several technologies can be used for this purpose. Magnetic trackers, such as manufactured by Ascension, can measure accurately 6 degrees of freedom of a hand-held device (the rangefinder) equipped with a sensor. The working volume of such systems is typically up to several meters and is not sufficient for most of the investigations.
Optical trackers, such as Optotrak developed by NDIGITAL, use a calibrated array of cameras to track special targets that may be attached to the hand-held device. However, these cameras must be installed on rigid supports and calibrated before use; the targets must be visible by multiple cameras at the same time. The number of required cameras and lengthy setup process is not suitable for investigations.
Systems that rely on Global Navigation Satellite System (GNSS) receivers, compasses and inclinometers to estimate the location and orientation of the rangefinder do not require any additional infrastructure in the scene. However, such systems require reliable GNSS signals and compass measurements and must be operated outdoors and at suitable distance from buildings, trees and objects that may affect the magnetic field. Toorenberg and Hartman independently disclose systems based on this principle for use in surveying.
A similar system with an integrated infra-red camera, IR513 Multifunctional Handheld Thermal Camera, is available from Armstrong Optical. Different technologies have been developed for estimating location of pedestrians.
NavShoe developed by InterSense uses foot-mounted inertial sensors to estimate the motion of a person wearing the system. Ojeda and Borenstein [Ojeda] developed a similar system to provide a location and use a second inertial sensor to provide relative orientation between the foot-mounted sensor and a hand-held device.
Other pedestrian localisation systems rely on pre-existing infrastructure in the buildings. Several solutions based on WiFi networks have been developed to provide an approximate location of a hand held detector/smart phone inside buildings. These systems provide only coarse location and require that the networks are fully mapped before use and are fully operational when the system is in use. Special Radio Frequency beacons can be deployed inside and outside the buildings and used for localisation. Radio Frequency Identification (RFID) tags may be placed throughout buildings and used for localisation but they must be placed and surveyed before they can be used operationally.
Conducting investigations requires an ability to operate in scenes not necessarily equipped with such infrastructure and installing it after the event poses many practical challenges: installation time and cost, and possibility for contaminating the scene and exposing investigators to hazards present in the scene.
During investigations, images captured by each camera and measurements collected by each device are saved in its own internal storage separately. The data is often represented in different data formats, and are not spatially linked to the other device data. This makes it difficult for the investigators to understand quickly the relationship between the data. Assigning data to specific locations manually is possible but is labour intensive and error prone.
The drawbacks of existing technologies include: need for infrastructure installed and calibrated before it can be used, short range of operations or requirement for a clear line of sight, reliable GNSS signal and compass readings. The data must be collected and organized in a way that is easy for data searching and data mining during and after the investigation. The invention described in this document addresses many of the above limitations.